Multifocal ophthalmic lenses and related methods

ABSTRACT

A multifocal ophthalmic lens wherein a first surface of the lens is shaped to form a surface power map and a second surface of the lens is shaped to form a second surface power map. The first surface power map and the second surface power map together form a lens power map. The first surface power map, the second surface power map, or the lens power map comprises a spiral. The spiral has a variation across at least a portion of the lens. Methods of making and using such lenses are also provided.

This application claims the benefit under 35 U.S.C. § 119(e) of priorU.S. Provisional Patent Application No. 63/017,975, filed Apr. 30, 2020,which is incorporated in its entirety by reference herein.

TECHNICAL FIELD

The present invention concerns multifocal ophthalmic lenses and relatedmethods. More particularly, but not exclusively, this invention concernsa multifocal ophthalmic lens, with a lens power map comprising a spiral,wherein the spiral has a variation across a portion of the lens. Theinvention also concerns methods of making and using such lenses.

BACKGROUND

In the context of the present disclosure, a multifocal ophthalmic lensis an ophthalmic lens which simultaneously provides focussing to morethan one distance. This is typically achieved by subdividing theophthalmic lens into a plurality of regions. Regions in a first subsetof the plurality of regions are provided with a first lens power,corresponding to a first focussing distance (for example distancevision). Regions in a second subset of the plurality of regions areprovided with a second lens power, corresponding to a second focussingdistance (for example near vision).

In multifocal contact lenses, the plurality of regions are typicallyformed as concentric circles centred on the optical axis of the contactlens, with the concentric circles alternating between the first lenspower and the second. Thus, the power map of an optic zone of a typicalmultifocal contact lens comprises at least two alternating concentriccircles of a first and second lens power. However, such contact lensescan cause difficulties for wearers in changeable light conditions. Inlower light conditions, the pupil of the wearer's eye dilates in orderto provide a larger aperture for incident light, increasing the amountof light received into the eye and thereby providing improved low-lightvision. As conditions brighten, the pupil constricts to provide asmaller aperture and thereby limit the amount of light received into theeye. As the wearer's pupil dilates and constricts, the number of theconcentric rings on the contact lens which are positioned across thewearer's entrance pupil will also vary. As the pupil dilates, a greaternumber of the concentric rings will be positioned across the wearer'sentrance pupil. Likewise, as the pupil constricts, fewer of theconcentric rings will be positioned across the wearer's entrance pupil.Because the concentric rings alternate between the first lens power andthe second lens power, the ratio of the first lens power to the secondlens power positioned across the wearer's entrance pupil will vary asthe wearer's pupil constricts and dilates. As the pupil constricts, thequantity of only one of near and distance focussing is reduced until thepupil has constricted to the diameter of the next smallest concentriccircle. At this point, the quantity of only the other of the near anddistance focussing is reduced until the pupil has constricted to thediameter of the next smallest concentric circle again. This cyclerepeats as the pupil constricts, causing variation in the ratio of thenear focussing to the distance focussing as the pupil constricts. Itwill be appreciated that the same effect occurs in reverse as the pupildilates. These variations in the ratio of near to distance focussing cancause distraction to the wearer and even a loss of multifocal vision.Generally, the more constricted the wearer's pupil, the more exacerbatedthis variation in the ratio. Therefore, in bright conditions inparticular when the pupil constricts to near to its minimum size,wearers of such multifocal contact lenses may find that the ability ofthe multifocal contact lens to provide high acuity in both near anddistance vision is impaired. This effect is exacerbated further fortwo-zone multifocal contact lenses, which are one of the more prevalentdesigns of multifocal contact lens. Two-zone multifocal contact lensescomprise an inner circle of a first lens power and a single surroundingperipheral ring of a second lens power. Thus, the more the pupil of awearer of such a contact lens constricts, the less of the second lenspower is positioned across the wearer's entrance pupil. In some cases,the pupil may even constrict to the extent that none of the second lenspower is positioned across the wearer's entrance pupil, causing acomplete loss of multifocal vision. Other multifocal contact lenses mayutilize a similar principle but instead of alternating concentric ringsmay include an aspheric power profile to provide a more gradualtransition from near viewing powers to distance viewing powers comparedto alternate ring embodiments.

The present invention seeks to mitigate the above-mentioned problems.Alternatively or additionally, the present invention seeks to provide animproved multifocal ophthalmic lens.

SUMMARY

The present invention provides, according to a first aspect, amultifocal ophthalmic lens. A first surface of the ophthalmic lens isshaped to form a first surface power map. A second surface of theophthalmic lens is shaped to form a second surface power map. The firstand second surface power maps together form a lens power map. The firstsurface power map, the second surface power map, and/or the lens powermap comprises a spiral. The spiral has a variation across at least aportion of the lens.

A contact lens having a power map comprising a spiral can provide a morestable ratio of near vision focussing to distance vision focussing inthe presence of changes in the pupil size of the wearer. As lightconditions change, the wearer's pupil will dilate and constrict in orderto regulate the amount of light received into the eye. As conditionsbrighten, the pupil constricts to reduce the amount of light allowedinto the eye. As conditions darken, the pupil dilates to allow morelight into the eye. Multifocal contact lenses of the prior art may usealternating concentric rings of near and distance focussing, for examplea central circle of distance focussing surrounded by a peripheral circleof near focussing. Alternatively, existing multifocal contact lenses mayuse aspheric power profiles within the optic zone. As discussed above,these contact lenses suffer from variation in the ratio of nearfocussing to distance focussing provided across the wearer's entrancepupil as the wearer's pupil dilates and constricts. These variations cancause distraction to the wearer and even a loss of multifocal vision.

A spiral power map as disclosed herein can provide a constant ratio ofnear focussing to distance focussing across the full range of diametersincluding the spiral map. Thus, a contact lens having a spiral power mapcan maintain either a substantially constant ratio (where the spiralcovers the whole of the optic zone of the lens) or a monotonicallyvarying ratio (where the spiral covers only a radial sub-portion of theoptic zone of the lens) of near to distance focussing as the pupilconstricts or dilates. Thus, a contact lens having a spiral power mapprovides improved multifocal vision in the presence of variable lightingconditions.

It will be appreciated by the skilled person that, where the power mapvaries smoothly (for example, as a sinusoid), the power map willcomprise lens powers other than simply a first lens power correspondingto near vision and a second lens power corresponding to distance vision.In such a case, the power map will also comprise regions having lenspowers between the first and second powers (e.g., intermediate lenspowers). It will be appreciated that this does not affect or diminishthe advantage described above of providing a consistent and stablevariation in the add power positioned across the wearer's entrancepupil. It will be appreciated by the skilled person that this advantageis derived from the fact that, for a spiral power map, the compositionof add powers at a particular radius does not vary according to a radialdistance from the optical axis of the lens.

According to a second aspect of the invention there is also provided amethod of manufacturing a multifocal ophthalmic lens. The methodcomprises operating a lathe to shape a first surface of one of: a lens,a mould for a lens, or an insert for manufacturing a mould for a lens toform a first surface power map. The method further comprises operating alathe to shape a second surface of the lens mould or insert to form asecond surface power map. The first surface power map and the secondsurface power map together form a lens power map. The first surfacepower map, the second surface power map, or the lens power map forms aspiral, the spiral having a variation across at least a portion of thelens. That portion includes the optic zone of the lens.

In a third aspect of the invention there is also provided a method ofusing the multifocal ophthalmic lens described herein. The methods maybe effective in improving the vision of a presbyopic lens wearer (e.g.,a person 40 years old or older). Alternatively, the methods may beeffective in reducing progression of a refractive error, such asreducing the progression of myopia or hyperopia. When the present lensesare used to reduce the progression of myopia, the methods include a stepof providing the ophthalmic lenses to a person whose eyes are able toaccommodate. Embodiments of the methods may include a step of providingthe ophthalmic lenses to a person that is from about 5 years old toabout 25 years old. The providing can be performed by an eye carepractitioner, such as an optician or optometrist. Alternately, theproviding can be performed by a lens distributor that arranges for thedelivery of the ophthalmic lenses to the lens wearer.

It will of course be appreciated that features described in relation toone aspect of the present invention may be incorporated into otheraspects of the present invention. For example, the method of theinvention may incorporate any of the features described with referenceto the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying schematic drawings ofwhich:

FIG. 1 shows a contact lens according to example embodiments of theinvention;

FIG. 2 shows a power map of a first surface of an optic zone of acontact lens according to a first embodiment of the invention;

FIG. 3 shows a lens power map of a first surface of an optic zone of acontact lens according to a second embodiment of the invention;

FIG. 4 shows a lens power map of the optic zone of a contact lensaccording to a third embodiment of the invention;

FIG. 5 shows a flow chart illustrating the steps of a method accordingto a fourth embodiment of the invention;

FIG. 6 shows a spectacle lens according to example embodiments of theinvention.

DETAILED DESCRIPTION

The present invention provides, according to the first aspect, amultifocal ophthalmic lens. A first surface of the lens is shaped toform a first surface power map. A second surface of the lens is shapedto form a second surface power map. It will be appreciated by theskilled person that the variation of a surface comprises a variation inthe curvature of the surface. The first and second surface power mapstogether form a lens power map. The first surface power map, the secondsurface power map, and/or the lens power map comprises a spiral, thespiral having a variation across at least a portion of the lens.

It will be appreciated that either of the first surface power map andthe second surface power map may have a substantially constant power of+0 D across the power map. For the purposes of this description, therespective surface of the lens is still considered to form a surfacepower map, even though that surface power map ultimately provides nofocussing or vision modification.

It may be that the ophthalmic lens is a contact lens. Alternatively, theophthalmic lens may be an intraocular lens or a spectacle lens.

It may be that the first surface varies across an optic zone of the lensto form the first surface power map. Similarly, it may be that thesecond surface varies across the optic zone of the lens to form thesecond surface power map. Thus, it may be that the portion of the lenscorresponds to an optic zone of the lens.

It will be appreciated that the lens will comprise an optic zone, whichprovides vision correction. Contact lenses and intraocular lensesaccording to embodiments of the invention may also comprise asurrounding peripheral zone, which provides no additional focussing orvision correction. In such embodiments, the peripheral zone may servemerely to help maintain the contact lens in position on or in thewearer's eye. Thus, it will be appreciated by the skilled person thatthe surface power map is defined by the profile of the first surfaceacross the optic zone of the lens. The profile of the lens surfaceoutside of the optic zone (for example, in a peripheral zone) is not, inthe context of the present invention, to be treated as defining thesurface power map. Similar considerations also apply to intraocularlenses, which may also comprise an optic zone and (optionally) aperipheral zone.

It may be that the optic zone of a contact lens according to embodimentsof the present invention has a diameter of between 4 mm and 9 mm,depending on the type of contact lens. For example, the diameter of theoptic zone may be about 5 mm, or about 6 mm, or about 7 mm, or about 8mm. The diameter of the optic zone of the contact lens may be between 7mm and 9 mm. The optic zone includes an optical axis that corresponds tothe geometric centre of the optic zone.

In the case of spectacle lenses, the entire lens may serve to providevision correction, rather than just a portion of the lens. Thus, theophthalmic lens may be a spectacle lens. It may be that the firstsurface is shaped across the whole of the lens to form the first surfacepower map.

It may be that the spiral has a first periodic component, in a radialdirection extending outwards from the centre of the portion, and asecond periodic component, in an azimuthal direction about the centre ofthe portion. It may be that the first and second components are eachformed on a same one of the first and second surface.

The azimuthal direction is to be understood to refer to rotation aboutthe centre of the portion. Thus, a movement in the azimuthal directionequates to a change in angular position about the centre of the portion.It will be appreciated that, in such embodiments, the variation of thepower map which forms a spiral is the sum of the first and secondperiodic components.

It may be that one or both of the first and second periodic componentsare of constant magnitude across the portion.

It may be that the first periodic component (in the radial direction)has a period of greater than 100 microns. It may be that the secondperiodic component has a period of greater than 6 degrees. It may bethat the period of the first periodic component is greater than 200microns, preferably greater than 400 microns, and more preferablygreater than 800 microns. The period of the first periodic component maybe less than 2 mm, preferably less than 1.5 mm, more preferably lessthan 1 mm. It may be that a period of the second periodic component (inthe azimuthal direction) is greater than 6 degrees, preferably isgreater than 9 degrees, preferably greater than 18 degrees, and morepreferably greater than 36 degrees. The period of the second periodiccomponent may be less than 180, preferably less than 90, more preferablyless than 45 degrees.

Thus, in embodiments, it may be that the first periodic component has aperiod of greater than 100 microns and the second periodic component hasa period of greater than 6 degrees, preferably greater than 9 degrees,more preferably greater than 18 degrees, and yet more preferably greaterthan 36 degrees. In other embodiments, it may be that the first periodiccomponent has a period of greater than 200 microns and the secondperiodic component has a period of greater than 6 degrees, preferablygreater than 9 degrees, more preferably greater than 18 degrees, and yetmore preferably greater than 36 degrees. In other embodiments, it may bethat the first periodic component has a period of greater than 400microns and the second periodic component has a period of greater than 6degrees, preferably greater than 9 degrees, more preferably greater than18 degrees, and yet more preferably greater than 36 degrees. In otherembodiments, it may be that the first periodic component has a period ofgreater than 800 microns and the second periodic component has a periodof greater than 6 degrees, preferably greater than 9 degrees, morepreferably greater than 18 degrees, and yet more preferably greater than36 degrees.

It may be that the variation of the spiral comprises an offset in power.The offset may change according to a radial distance from the centre ofthe portion. In embodiments, the offset may comprise one of theplurality of components. Thus, the plurality of components may furthercomprise an offset component which varies (for example, linearly,exponentially, or monotonically) with a radial distance from the centreof the lens. For example, it may be that the offset provides an addpower which decays, for example linearly, radially outwards from thecentre of the portion.

It may be that a peak power of one or more arms of the spiral variesaccording to one or both of: a radial distance from the centre of theportion and an azimuthal position about the centre of the portion. Itmay be that a magnitude of the periodic components changes according toone or both of: a radial distance from the centre of the portion and anazimuthal position about the centre of the portion.

It may be that a peak power of each arm of the spiral does not vary withradial distance from the centre of the portion. It may be that the peakpower of at least one arm of the spiral differs from that of the otherarms. Thus, it may be said that each arm of the spiral provides adifferent lens power. It may therefore be that multifocal vision isprovided by the arms of the spiral. It may be that the peak power ofeach arm of the spiral differs from that of the other arms. It will beappreciated that such a feature may be characterised as a variation ofthe periodic components with respect to both radial distance from thecentre of the portion and azimuthal position about the centre of theportion. Thus, it may be that the periodic components vary with respectto both radial distance from the centre of the portion and azimuthalposition about the centre of the portion such that the peak power of atleast one arm (for example, each arm) of the spiral differs from that ofthe other arms.

It may be that the power of the first surface power map varies smoothlyacross the portion. It may be that the power of the second surface powermap varies smoothly across the portion. Thus, it may be that theperiodic components vary smoothly (for example, as a sinusoid or arounded square wave). It may be that surface power maps each variescontinuously, without any discontinuities. It may be that the powervaries across the portion at a rate of less than 80 D/mm, preferablyless than 40 D/mm, more preferably less than 20 D/mm. It may be that thesurface varies smoothly across the portion. It may be that surfacevaries continuously, without any discontinuities. Varying the powersmoothly can result in a lens surface profile which is easier tomanufacture using a lathe. It will be appreciated by the skilled personthat manufacturing an ophthalmic lens using a lathe may comprise using alathe to shape a surface of one or more of a lens (for example a contactlens), a mould for a lens (for example a mould for a contact lens), andan insert for a lens mould (for example an insert for a contact lensmould). Sharp transitions and features can be difficult to achieve usinga lathe. Therefore, lenses having such features are often notreproducible with the intended or required definition when manufacturedusing a lathe. Thus, it will also be appreciated that the term smoothlyin this context means smooth enough to enable the desired shaping of thesurface of a lens, a mould for a lens, or an insert for a lens mouldusing a lathe.

The power may vary as a square wave in one or both of the radial andazimuthal directions. The power may vary as a rounded square wave in oneor both of the radial and azimuthal directions. The power may vary as asinusoid in one or both of the radial and azimuthal directions.

The first and second periodic components may vary as one of: a squarewave, a sinusoid, and a rounded square wave. The period of one or bothof the first and second periodic components may be substantiallyconstant across the portion of the lens. Embodiments of the invention inwhich the first and second periodic components have a substantiallyconstant period across the portion yield a lens surface profile which iseasier to manufacture using a lathe compared to embodiments in which theradial and angular variations are not constant. In the case of contactlenses according to embodiments of the invention, one or both of thefirst and second periodic components may have a substantially constantperiod from the optic zone perimeter in towards the optic axis of theoptic zone.

It may be that the power variation in each of the radial and angulardirections is associated with a respective waveform. In addition, thepower distributions of the waveforms may be symmetrical with asubstantially equal balance between near vision correction and distancevision correction. Alternately, the power distribution may be biasedtowards either distance vision correction or near vision correction.Thus, the power distributions of the waveforms may be asymmetric in oneor both of the radial direction and the angular direction.

The period of one or both of the first and second periodic componentsmay change according to either or both of a radial distance from thecentre of the portion of the lens and an azimuthal position about thecentre of the portion. Embodiments of the invention in which the periodof one or both of the first and second periodic components changeaccording to position on the lens can provide a lens in which thecharacteristics of the spiral (for example its rate of rotation or armwidth) differ in different regions of the lens.

Changes in the period of the first periodic component (that is theperiodic component in the radial direction) may be separated by ablending region, for example of smoothly (for example, linearly) varyingperiod. The blending region may therefore comprise a concentric ring ofsmoothly (for example, linearly) varying period between a first regionhaving a first period of radial variation and a second region having asecond period of radial variation. Alternatively, the blending regionmay comprise a region of smoothly (for example, linearly) varying lenspower. Thus, the blending region may provide a smooth transition betweenregions of different period radial variation. It may be that regions ofdifferent period radial variation are separated by two blending regionsand an intervening region of substantially constant lens power. Theblending region may have a width (in plan view) from about 25micrometers to about 200 micrometers.

The spiral may comprise more than two arms, preferably more than 4 arms,more preferably more than 8 arms, yet more preferably more than 16 arms.It will be appreciated by a person skilled in the art that the period ofthe second periodic component will determine the number of arms on thespiral.

The period of the first periodic component may be between 24 mm and 2mm. The period of the first periodic component may be between 16 mm and4 mm. It may be that each arm of the spiral twists through between aquarter of a rotation and 40 rotations. It will be appreciated by aperson skilled in the art that the number of rotations that an arm ofthe spiral twists through is determined by the period of the firstperiodic component and a radius (or size) of the portion of the lens. Itwill be appreciated that references to the radius of the portion (forexample, an optic zone of a contact lens) refer to a distance of half ofa plan view diameter of the portion. In this context, a plan view isintended to be taken as a view along the optical axis of the lens.

It may be that a ratio of the period of the first periodic component tothat of the second periodic component is greater than 0.1 mm: 6°. It maybe that each arm of the spiral is wider than 0.1 mm, preferably widerthan 0.5 mm, more preferably wider than 1 mm. It may be that each arm isbetween 0.1 mm and 3 mm wide. It may be that each arm is between 0.25 mmand 2 mm wide. It may be that each arm is between 0.5 mm and 1 mm wide.The width of the spiral arms are determined when viewing the power mapin plan view (i.e. along the optical axis of the lens), as shown in theaccompanying drawings. It will be understood by a person skilled in theart that a width of an arm at a given radius is defined as itsperpendicular width (i.e. its width in the direction perpendicular tothe given radius). The width of the arm is, in this context, defined asthe distance between two points immediately adjacent each side of thearm, both points having either a maximum or a minimum gradient, betweenwhich the power undergoes a single positive or negative excursion. Theskilled person will appreciate that such a definition of width providesa straight-line measurement of arm width along a tangent to a circle ofthe given radius. The skilled person will further appreciate that ameasurement of width under this definition will differ from ameasurement of the width of an arm taken as an arc of a circle havingthe given radius. Unlike a width measurement under the straight-linewidth definition, such an arc-based measurement would be proportional tothe period of the second periodic component. The magnitude of thedifference between the widths obtained by these two methods will dependon the period of the second periodic component in the particular case athand.

It may be that each arm of the spiral extends from the centre of theportion of the lens to the periphery of the portion. Contact lensesaccording to embodiments of the invention in which the arms of thespiral extend from the centre of the portion to the periphery of theportion can provide a substantially constant ratio of the first lenspower to the second lens power in the presence of varying pupildilation. Such embodiments thereby provide high acuity multifocal visionin a wide range of light conditions.

It may be that a twist rate of the spiral varies according to a radialdistance from the centre of the portion. The twist rate of the spiralwill be understood to mean the rate at which the arms of the spiralrotate about the centre of the spiral (i.e. the number of rotations ofthe arms about the centre of the spiral across a given radial distance).It will be appreciated that a change in the twist rate of the spiral maybe the result of a non-proportional change in the period of the firstperiodic component compared to a change in the period of the secondperiodic component (for example, by changing the period of the firstperiodic component whilst maintaining the period of the second periodiccomponent unchanged). It may be that a width of one or more arms of thespiral differs from a corresponding width of the other arms of thespiral. It will be appreciated that such a feature may be defined as theperiodic components providing the periodic components with a varyingduty cycle across the portion.

It will be appreciated that the lens will have a means lens power.Furthermore, it will be appreciated that the lens will be dividedbetween a first area of the lens having a lens power greater than themean and a second area of the lens having a lens power less than themean. It may be that a ratio of the first area to the second area isbetween 10:1 and 1:10. It may be that a ratio of the first area to thesecond area is between 5:1 and 1:5. It may be that a ratio of the firstarea to the second area is between 3:1 and 1:3. It may be that a ratioof the first area to the second area is between 2:1 and 1:2. It may bethat a ratio of the first area to the second area is approximately 1:1.

The portion of the lens, which may be an optic zone, may comprise acentral region and an outer region. The central region may immediatelysurround the optical axis of the lens. The central region may be offsetfrom the geometric centre of the lens. For example, it may be desirableto offset the central region from the geometric centre of the lens toallow the optical axis of the offset central region to align with thepupil of the lens wearer due to natural decentration of the lens on theeye. The outer region may surround (for example, immediately surround)the central region. It may be that the power of the central region doesnot vary periodically across the central region (for example, havingsubstantially constant lens power across the central region). The lenspower map in the outer region may comprise the spiral. Thus, it may besaid that the outer region comprises the spiral. Providing a contactlens having an optic zone with a central region having a lens powercorresponding to distance vision and free from periodic power variationcan ensure that the wearer maintains high acuity distance vision even inbright conditions. For example, this may be particularly advantageous tothe wearer when driving. Alternatively, it may be that the centralregion comprises the spiral, and the power of the outer region does notvary periodically across the outer region (for example, havingsubstantially constant lens power across the outer region).

A contact lens may include a peripheral zone, which surrounds the opticzone and which provides no additional focussing or vision correction andserves merely to help maintain the contact lens in position on thewearer's eye. When worn on an eye, the contact lens rests on the corneaand the optic zone approximately covers the pupil of the wearer, in theconventional manner. Thus, it will be understood that contact lensesaccording to the invention may comprise an optic zone and a surroundingperipheral zone. The optic zone provides vision correction. Theperipheral zone does not provide any vision correction, but theperipheral zone may provide other functions (such as helping to maintainthe contact lens in position on the eye). The surfaces of the lenswithin the optic zone provide the first and second power maps, andthereby also the lens power map. The optic zone may therefore optionallycomprise central, outer, and transition regions as described above. Theoptic zone may also comprise one or more blending regions as previouslydescribed.

The diameter of the central region may be less than 50%, preferably lessthan 40%, more preferably less than 30%, of that of the portion. Thus,in contact lenses according to embodiments of the invention, thediameter of the central region may be less than 50%, preferably lessthan 40%, more preferably less than 30%, of that of the optic zone ofthe contact lens. The central region may be smaller than the minimumpupil size of a wearer of the contact lens. Embodiments of the inventionhaving a central region which is smaller than the minimum pupil size ofthe wearer can maintain high acuity near and distance vision in thepresence of varying light conditions.

The power of the central region may be substantially constant (forexample, the power can vary by less than 0.25 dioptres (D) from thenominal power across the central region). The central region may have alens power corresponding to distance vision. Contact lenses according toembodiments of the invention in which the central region has asubstantially constant lens power corresponding to distance vision canprovide high acuity distance vision in bright light conditions, when thepupil is at its minimum size. High acuity distance vision is generallymore useful to the wearer than high acuity near vision in bright lightconditions because such conditions generally correspond to daytimeoutdoor environments where the wearer typically has greater need fordistance vision than for near vision. Alternatively, the central regionmay have a lens power corresponding to near vision. Furthermore, thecentral region may have a lens power that is more positive than the nearvision correction power required by the lens wearer. For example, thepower of the central region may be +0.25 D to +1.25 D more positive thanrequired by an eye for near vision correction.

The lens may comprise a transition region. The transition region maysurround the central region. The outer region may surround thetransition region. Thus, the transition region may be positioned betweenthe central and outer regions. It may be that the power of thetransition region varies to provide a smooth transition between thecentral and outer regions. Embodiments of the invention providing asmooth transition between the central and outer regions can enableeasier manufacture using a lathe of a lens, a mould for such a lens, oran insert for such a lens mould. Thus, it will be appreciated by theskilled person that smooth in this context means that the lens profilemust be smooth enough to be produced using a lathe.

It may be that the spiral is formed entirely on the first surface (i.e.the spiral is formed entirely by the first surface power map). Thus, itmay be that the second surface power map does not vary periodicallyacross the portion of the lens. Alternatively, the spiral may be formedentirely on the second surface (i.e. the spiral is formed entirely bythe second surface power map). Thus, it may be that the first surfacepower map does not vary periodically across the portion of the lens.Alternatively, the spiral may be formed by the first and second surfacestogether (i.e. the spiral is formed by the superposition of the firstand second surface power maps). Contact lenses according to embodimentsof the invention in which the optic zone comprises a spiral lens powermap can provide a substantially constant ratio of the first lens powerto the second lens power in the presence of varying pupil size.

It will be appreciated that either of the first surface power map andthe second surface power map may have a substantially constant power of+0 D across the power map. For the purposes of this description, asurface of the lens is still considered to form a surface power map,even if that surface power map ultimately provides no focussing orvision modification.

The first surface power map may vary substantially periodically radiallyoutwards from the centre of the portion. The second surface power mapmay vary substantially periodically radially outwards from the centre ofthe portion. The lens power map may vary substantially periodicallyradially outwards from the centre of the portion. A period of the radialvariation of the surfaces may be greater than 100 microns, preferablygreater than 200 microns, more preferably greater than 400 microns, andyet more preferably greater than 800 microns.

The first surface power map may vary substantially periodicallyazimuthally about the optical axis of the lens. The second surface powermap may vary substantially periodically azimuthally about the opticalaxis of the lens. The lens power map may vary substantially periodicallyazimuthally about the optical axis of the lens. A period of theazimuthal variations of the surfaces may be greater than 6 degrees,preferably greater than 9 degrees, more preferably greater than 18degrees, and yet more preferably greater than 36 degrees.

The periods and phases of the radial and azimuthal variations of thesecond surface may be the same as those of the first surface. It will beappreciated that the periods of the azimuthal and radial variations ofthe first surface power map need not necessarily be the same as those ofthe second surface power map. The first surface power map and/or thesecond surface power map may comprise a spiral, for example a spiralhaving a variation across the portion. The second surface power map maycomprise a spiral matching a spiral of the first surface power map. Insuch embodiments, the power map of the lens as a whole also comprises aspiral. Embodiments of the invention comprising contact lenses with aspiral lens power map can provide a substantially constant ratio of thefirst lens power to the second lens power in the presence of varyingpupil size.

It may be that the spirals provided by the first and second surfacestwist in opposing directions. Thus, the first and second surface powermaps can be said to comprise counter-rotating spirals. The spiralsprovided by the first and second surface power maps may be the same butfor the opposing twist directions. Embodiments of the invention in whichthe first and second surface power maps comprise counter-rotatingspirals can give a lens power map which approximates a dartboard-likepattern of alternating annular rings. It will be appreciated by a personskilled in the art that the lens power map is formed by thesuperposition of the first and second surface power maps. Thus, it willalso be appreciated that the pseudo-dartboard pattern is provided by thecombination of the first and second surface power maps, each of whichretains the previously described benefits of ease of manufacture. Thus,such embodiments can enable easier manufacture of a lens having apseudo-dartboard power map using a lathe.

The lens power map may comprise a plurality of sections. Sections in theplurality of sections may provide a first power corresponding todistance vision or a second power corresponding to near vision. Thesections may be arranged on the lens such that they alternate radiallyand/or azimuthally between the first power and the second power.Accordingly, the first power may be between 0 dioptres (D) and −10 D.The first power may be from −0.25 D to −6.00 D. The second powerprovided in the present lenses may be more positive than the first powerof the lens, for example, the second power may be from 1 D to 5 D morepositive than the first power. The second power may be 1 D to 4 D morepositive than the first power. The second power may be 2 D to 3 D morepositive than the first power. The second power may vary, such as mayoccur when providing discrete sections of defocus with more positivepower than the first power, such that some of the section may have asecond power of +1 D, some sections may have a second power of +2 D, andsome sections may have a second power of +3 D. The variation of thesecond power may occur within the same arm, or the variation of thesecond power may occur in different arms.

It may be that, at a pre-determined radial distance from the centre ofthe portion, the spiral changes its direction of rotation. Thus, it maybe that a first section of the lens comprises a clockwise rotatingspiral and a second section of the lens comprises an anti-clockwiserotating spiral. Such sections may be formed as concentric rings, forexample centred on the centre of the portion. Sections of the lenshaving different directions of rotation may be separated by anintervening section of substantially constant lens power. It may be thatthe lens comprises more than one change in the direction of rotation ofthe spiral (for example, with each change in direction having anintervening section of substantially constant lens power).

The multifocal lens may be a myopia control lens, and the multifocallens may be configured to reduce the progression of myopia in a personwhose eyes are able to accommodate. The multifocal lens may be suitablefor providing vision correction, and the multifocal lens may beconfigured to provide distance vision correction and near visioncorrection to a person whose eyes are unable to accommodate sufficiently(e.g., a person 40 years old or greater).

A contact lens according to the invention may comprise a ballast toorient the lens when positioned on the eye of a wearer. Such a ballastmay be provided by a peripheral zone of the contact lens. It may be thatthe contact lens provides particular benefit to the wearer in a givenorientation. Embodiments of the invention incorporating a ballast intothe contact lens will, when placed on the eye of a wearer, rotate underthe action of the wearer's eyelid to a pre-determined angle of repose;for example the ballast may be a wedge and the rotation may result fromthe action of the eyelid on the wedge. By positioning the ballast in thecontact lens, it is possible to ensure that the angle of reposecorresponds to a lens orientation providing particular benefit to thewearer.

The present invention provides, according to the second aspect, a methodof manufacturing a multifocal ophthalmic lens (for example a contactlens). The method comprises operating a lathe to shape a first surfaceof one of: a lens (for example a contact lens), a mould for a lens (forexample a mould for a contact lens), or an insert for manufacturing amould for a lens (for example an insert for a mould for a contact lens).The first surface is shaped to form a first surface power map. Themethod further comprises operating a lathe to shape a second surface ofthe lens, mould or insert. The second surface is shaped to form a secondsurface power map. The first and second surface power maps together forma lens power map. The first surface power map, the second surface powermap, and/or the lens power map comprises a spiral, the spiral having avariation across at least a portion of the lens, mould or insert.

The first surface may be shaped such that the surface power map variessubstantially periodically both radially outwards from and azimuthallyabout the centre of the portion. It may be that a period of the radialvariation is greater than 100 microns. It may be that a period of theazimuthal variation is greater than 6 degrees.

It may be that the method comprises operating a lathe to shape thesurface of at least a portion of a lens. Alternatively or additionally,the method may comprise operating a lathe to shape the surface of atleast a portion of a mould for a lens. Alternatively or additionally,the method may comprise operating a lathe to shape the surface of atleast a portion of an insert for manufacturing of a mould for a lens. Itwill be appreciated by the skilled person that the further removed thesubject of the shaping by the lathe is from the lens, the less featuredefinition that will reproduced on the resulting lens. Thus, forexample, shaping the surface of a lens using a lathe enables moredefined surface features than will be achievable when using the lathe toshape the surface of a mould for a lens.

The method further comprises operating a lathe to shape a second surfaceof the portion of the lens, the mould, or the insert. The second surfacemay be shaped to vary across at least the portion to form a secondsurface power map comprising a spiral. The second surface may be shapedsuch that the second surface power map varies substantially periodicallyboth radially outwards from and azimuthally about the centre of theportion. A period of the radial variation may be greater than 100microns. A period of the azimuthal variation may be greater than 6degrees. The second surface may be shaped such that the second surfacepower map varies as a mirror image of the first surface. The secondsurface may be shaped such that the spiral formed by the first surfacepower map twists in the opposite direction to that formed by the secondsurface power map.

It may be that the lens is a contact lens. In such embodiments, theportion of the lens may correspond to an optic zone of the contact lens.In such cases, it will be appreciated that references to an optic zoneof a mould or an insert for a mould refer to the part of the mould whichcorresponds to the optic zone of a lens manufactured using that mould orinsert.

Lenses, for example contact lenses, according to the present inventioncan be formed by cast moulding processes, spin cast moulding processes,or lathing processes, or a combination thereof. As understood by personsskilled in the art, cast moulding refers to the moulding of a contactlens by placing a lens forming material between a female mould memberhaving a concave lens forming surface, and a male mould member having aconvex lens forming surface.

In embodiments in which the ophthalmic lens comprises a contact lens,the contact lens material, as it is used as a part of a contact lens oras an entire contact lens, is visually transparent (although it caninclude a handling tint). The contact lens material can be a hydrogelmaterial, a silicone hydrogel material, or a silicone elastomermaterial, as understood in the art. In other words, the present contactlenses can comprise, consist essentially of, or consist of a hydrogelmaterial, a silicone hydrogel material, or a silicone elastomermaterial. As understood in the field of contact lenses, a hydrogel is amaterial that retains water in an equilibrium state and is free of asilicone-containing chemical. A silicone hydrogel is a hydrogel thatincludes a silicone-containing chemical. Hydrogel materials and siliconehydrogel materials, as used herein, have an equilibrium water content(EWC) of at least 10% to about 90% (wt/wt). The hydrogel material orsilicone hydrogel material may have an EWC from about 30% to about 70%(wt/wt). In comparison, a silicone elastomer material, as used herein,has a water content from about 0% to less than 10% (wt/wt). Typically,the silicone elastomer materials used with the present methods orapparatus have a water content from 0.1% to 3% (wt/wt). Alternatively,examples of the present contact lenses can be made from rigid gaspermeable materials, such as polymethyl methacrylate (PMMA) and thelike.

The present methods may include a step of forming a contact lens in amoulding assembly, which comprises a first mould part and a second mouldpart assembled together. In the case of hydrogel lenses or siliconehydrogel lenses, the lenses can be made by polymerizing a hydrogel orsilicone hydrogel lens formulation that includes a polymerizationinitiator in a lens shaped cavity formed between the first mould partand the second mould part. For silicone elastomer lenses, the lenses canbe made by curing, vulcanizing, or catalysing, such as by hydrosylation,a liquid silicone elastomer material in a lens shaped cavity formedbetween the first mould part and the second mould part. The surface ofeach mould part that forms the contact lens shaped cavity may be convex,concave, planar or a combination of thereof. After formation of thecontact lens, the two mould parts are separated such that the contactlens remains attached to the surface of one of the mould parts. As aresult, a contact lens is provided on a surface of the first or secondmould part. In some other embodiments, it may be desirable to place thelens on a surface of a mould part that was not used to produce the firstlens member, but that may require additional steps to achieve thedesired alignment of the member to the mould part. The lenses may thenbe removed from the mould part to which they are attached, and furtherprocessed, such as by extraction and hydration, and inspected, andpackaged in a package and sterilized.

FIG. 1 shows a contact lens 10 according to embodiments of theinvention. The contact lens 10 comprises an optic zone 11 and aperipheral zone 13. The optic zone 11 comprises the part of the lensthrough which a wearer of the contact lens sees. The optic zone 11 formsa lens designed to provide vision correction to the wearer. Theperipheral zone 13 surrounds the optic zone 11 and does not provide anyvision correction to the wearer. The peripheral zone 13 may performother functions. For example, the peripheral zone 13 may serve to helpmaintain the contact lens on the wearer's eye. The peripheral zone 13may include a ballast in order to maintain a predetermined orientationof the contact lens on the wearer's eye.

The two surfaces of the contact lens are shaped such that they varyacross the optic zone 11 to form first and second surface power maps.The first and second surface power maps together form a lens power map.Thus, the optic zone can be said to provide a first surface power map, asecond surface power map, and a lens power map. Within the optic zonethe power maps may comprise one or more distinct regions. The examplecontact lens shown in FIG. 1 comprises a central region 15, an outerregion 17, and a transition region 19. The outer region 17 surrounds thetransition region 19. The transition region 19 surrounds the centralregion 15. The central region 15 and the outer region 17 may providediffering arrangements of lens power, such that they provide differentvision corrections. The transition region 19 may serve for provide asmooth transition between the central region 15 and the outer region 17.It will be appreciated that the contact lens illustrated in FIG. 1 isprovided merely as an example, and that other contact lenses accordingto the invention may include more or fewer regions. For example, somecontact lenses according to embodiments of the invention may omit thetransition region, or some contact lenses may even comprise only asingle region across the whole of optic zone 11. Other contact lensesaccording to embodiments of the invention may include additionalregions, for example formed as concentric circles.

According to a first example embodiment of the invention, there isprovided a multifocal contact lens. It will be appreciated thatalternative embodiments may comprise an intraocular lens or a spectaclelens. The multifocal contact lens comprises a first surface and a secondsurface. In this example embodiment, the first surface comprises anouter surface of the contact lens and the second surface comprises aninner surface of the contact lens. It will be appreciated by the personskilled in the art that the outer surface is the convex surface of thecontact lens adjacent to a wearer's eyelid and that the inner surface isthe concave surface of the contact lens adjacent the wearer's eye.

A portion of the first surface is shaped to form a first surface powermap. A corresponding portion (for example, an opposing portion) of thelens is shaped to form a second surface power map. Thus, it can be saidthat a portion of the lens comprises first and second surfaces, formingrespective first and second surface power maps. In this exampleembodiment, the portion corresponds to an optic zone of the contactlens. Thus, in this example embodiment, it can be said that a firstsurface of the optic zone forms the first surface power map and a secondsurface of the optic zone forms the second surface power map. It will beappreciated by the skilled person that the first surface power map showsthe modification to the overall contact lens power map provided by theshape of that surface. Thus, a contact lens having two surfaces (aninner surface and an outer surface) comprises two surface power maps,the combination of which determines the overall contact lens power map.

FIG. 2 shows the first surface power map 100. The first surface powermap 100 forms a spiral. The spiral varies across the portion, as isexplained in further detail below. The spiral comprises a plurality of(in this example 4) arms 101. Each of the arms 101 comprises one of apeak arm 101 a and a trough arm 101 b. It will be appreciated that apeak arm 101 a is an arm which constitutes a positive excursion of lenspower, and that a trough arm 101 b is an arm which constitutes anegative excursion of lens power.

The spiral can be considered to be formed by a summation of a pluralityof components. In this case, the plurality of components includes afirst periodic component in a radial direction extending outwards fromthe centre of the portion and a second periodic component in anazimuthal direction about the centre of the portion. In addition, theplurality of components further comprises an offset in power, the offsetchanging according to a radial distance from the centre of the portion.Thus, the spiral can be said to comprise a variation across the portion.In this example embodiment, the centre of the portion lies on theoptical axis of the lens. It will be appreciated that an optical axis ofa lens is equivalent to an optical axis of the optic zone of that lens.

In this example embodiment, the offset changes across the portion from+0 D at an inner part of portion to −3.0 D at the periphery of theportion. It will be appreciated that, in this example embodiment, whichincludes central and outer regions, the inner part of the lenscorresponds to the innermost part of the outer region. In this exampleembodiment, the offset varies linearly. In other embodiments, the offsetmay vary in other ways, for example exponentially and/or monotonically.The periodic components vary between +0 D and +3.0 D. It will beappreciated that the power at a given point of the first surface powermap is determined by the combination of the offset and the periodiccomponents. Other embodiments of the invention may include componentsother than simply an offset and radial and azimuthal periodiccomponents. It will be appreciated that, in such embodiments, theoverall surface power map is formed by the combination of all of thosecomponents. Thus, in this example embodiment, the power of a point onthe surface power map varies across the portion from −3.0 D up to +3.0D. It will also be noted that, due to the offset in power, the variationof the power is dependent on the position on the portion. Specifically,the power varies between −3.0 D and +0 D at the periphery of theportion, and between +0 D and +3.0 D at the inner part of the portion.Thus, the multifocal contact lens of this example embodiment can beconsidered to have a base lens power, which varies across the portionfrom +0 D at the centre of the portion to −3.0 D at its periphery, andan add power of +3.0 D provided by the periodic components. Such acontact lens may be suitable for a patient who suffers from both myopiaand presbyopia. The −3.0 D base lens power serves to correct thewearer's distance vision, whilst the +3.0 D add power serves to correctfor the wearer's near vision when the wearer is not able to sufficientlyaccommodate. It will be appreciated by a person skilled in the art thatthe specific values of the first lens power and the second lens power(and therefore the base lens power and add power) provided are purelyexamples, and that the actual values used in a given situation will bedetermined by the needs of the intended wearer.

In this example embodiment, the period of the radial variation is 1.2 mmand the period of the azimuthal variation is 90 degrees. However, itwill be appreciated that, in alternative embodiments, other periods ofthe radial and/or azimuthal variation may be used.

In this particular embodiment, the power varies smoothly across thefirst surface power map 100, substantially as a sinusoid in both theradial and azimuthal directions. Having the surface power map varysmoothly across the portion of the lens provides for easier manufactureusing a lathe of the contact lens or of apparatus (for example, a mouldor an insert for a mould) for manufacturing the contact lens. However,in alternative embodiments, the power may vary according to otherwaveforms. For example, the power may vary as a square wave or as arounded square wave in one or both of the radial and azimuthaldirections. Thus, in alternative embodiments, the power need notnecessarily vary smoothly across the portion of the lens.

In this example embodiment, the positive and negative excursions of theperiodic components are of equal length, such that they can be said tohave a 50% duty cycle. Alternative embodiments comprise periodiccomponents having other duty cycles. Thus, in such embodiments, thepositive excursion may be of a different length than the negativeexcursion. Such embodiments can bias the periodic components towards aparticular lens power, for example by providing a greater quantity of afirst lens power than a second.

It will be appreciated that the width of the arms 101 of the spiral isdetermined at least in part by the ratio of the period of the radialvariation to that of the azimuthal variation. In this exampleembodiment, each arm 101 of the spiral is approximately 500 micronswide. It will be appreciated that alternative embodiments mayincorporate arms 101 having different widths. It will also beappreciated that the width of an arm 101 is defined as its perpendicularwidth. In this embodiment, all of the arms of the spiral are of equalwidth however, in other embodiments, one or more arms of the spiral maybe of a different width to the other arms of the spiral.

Similarly, in this example embodiment, the periods of the first andsecond periodic components are each substantially constant across theportion. However, in alternative embodiments, the period of at least oneof the first and second periodic components may change according to oneor both of a radial distance from the centre of the portion and anazimuthal position about the centre of the portion.

In alternative embodiments, the period of the second periodic componentis less than 180°. It will be appreciated by a person skilled in the artthat the period of the second periodic component determines the numberof arms 101 on the spiral. Thus, in such embodiments, the spiralcomprises at least two arms. It will therefore also be appreciated thatcertain values of the period of the second periodic component,specifically those which are unit fractions of 360 degrees, may beparticularly advantageous in that they allow for a surface power mapwithout azimuthal discontinuities.

In this example embodiment, each arm 101 of the spiral twists through anangle of 270 degrees (or 0.75 of a rotation). In alternative embodimentsof the invention, each arm 101 of the spiral may twist through between aquarter of a rotation (90 degrees) and 40 rotations. In this exampleembodiment, the arms of the spiral twist at a constant rate across theportion. Thus, the arms can be said to have a constant twist rate. Inother embodiments, the twist rate of the arms may vary across theportion.

In this particular embodiment, the first surface power map 100 comprisesa central region 103 and an outer region 105. The central region 103immediately surrounds the optical axis of the contact lens. The outerregion 105 surrounds the central region 103. The power of the centralregion does not vary periodically across the central region 103 and may,for example, be substantially constant across the central region 103.The outer region 105 comprises the spiral power map. In alternativeembodiments of the invention, each arm 101 of the spiral extends fromthe centre of the portion of the lens to the periphery of the portion.Thus, such embodiments do not comprise distinct central and outerregions.

As has been previously mentioned, in this example embodiment, theportion of the lens corresponds to the optic zone of a contact lens. Inthis example embodiment, the central region 103 has a diameter of 2 mm,which corresponds to 25% of the 8 mm diameter of the optic zone. Theoptic zone, through which the wearer sees, provides the first surfacepower map shown in FIG. 1 . The contact lens may in addition comprise asurrounding peripheral zone, which provides no additional focussing orvision correction and serves merely to help maintain the contact lens inposition on the wearer's eye. The diameter of the central region may beless than 25% of that of the optic zone. However, it will be appreciatedthat, in alternative embodiments of the invention, the diameter of thecentral region 103 may take other values. Similarly, it will beappreciated that the ratio of the diameter of the central region 103 tothat of the optic zone may also take other values. For example, thediameter of the central region 103 may be less than 30% of that of theoptic zone.

The central region 103 may be smaller than the minimum pupil size of awearer of the contact lens. Such embodiments maintain multifocal visioneven when the wearer's pupil constricts to its minimum size. If thecentral region 103 is larger than the minimum pupil size, when thewearer's pupil constricts to its minimum size, only the central region103 will be positioned across the wearer's entrance pupil. As the powerof the central region 103 does not vary as a spiral across the centralregion 103, the lens will not provide multifocal vision for any pupilsizes smaller than the central region 103.

Advantageously, in this example embodiment, the central region 103provides a lens power corresponding to distance vision. Generally,brighter conditions correspond to outdoors environments. Thus, thewearer's pupil is typically more constricted when outdoors than whenindoors. In addition, the wearer generally has greater need for distancevision when outdoors than when indoors. Having a central region 103 witha lens power corresponding to distance vision can allow the contact lensto provide high acuity distance vision even when the wearer's pupil isconstricted to its minimum size.

This example embodiment further comprises a transition region 107. Thetransition region 107 surrounds the central region 103. The outer region105 surrounds the transition region 107. The power of the transitionregion 107 varies to provide a smooth transition between the centralregion 103 and the outer region 105. It will be appreciated that such atransition region 107 is not essential and therefore that alternativeembodiments do not include a transition region 107. It will beappreciated that smooth, in this context, is defined as being smoothenough for the corresponding lens curvature to be reproduced by a lathe.In this example embodiment, the transition region is approximately 300microns wide. It will, however, be appreciated that other widths oftransition region may also be used.

It will be appreciated by the skilled person that the second surface ofthe portion of the contact lens (i.e. the second surface of the opticzone of the contact lens of this example embodiment) forms a secondsurface power map. In this example embodiment the second surface powermap does not vary periodically across the portion, providing asubstantially constant +0 D power across the portion. Therefore, thecontact lens has a lens power map which matches the first surface powermap. The contact lens therefore provides reduced variation in the ratioof near focussing to distance focussing as the wearer's pupil changessize.

Whilst in this example embodiment the first surface corresponds to theouter surface of the contact lens and the second surface corresponds tothe inner surface of the contact lens, a person skilled in the art willappreciate that, in alternative embodiments, the first surface maycorrespond to the inner surface and the second surface may correspond tothe outer surface. Thus, in embodiments, the inner surface comprises asurface power map forming a spiral and the outer surface comprises asurface power map having substantially constant power across the surfacepower map.

FIG. 3 shows a second multifocal contact lens according to a secondexample embodiment of the invention. The contact lens comprises a firstsurface power map 200 substantially as described in respect of the firstembodiment, but for the following features. The first surface power map200 of the second embodiment does not comprise an offset in power. Thus,the first surface power map can be said to comprise a base lens powerwhich is substantially constant across the portion. Furthermore, themagnitude of the spiral varies across the portion with respect to aradial distance from the centre of the portion. That is to say that amagnitude of each of the periodic components varies according to aradial distance from the centre of the portion. In this exampleembodiment, the magnitude of the periodic components is at its maximumat the innermost part of the outer region and decays linearly withradial distance from the centre of the portion. Thus, the spiral onceagain comprises a variation across the portion. The second surface powermap 200 is the same as that of the first embodiment. Thus, the lenspower map matches that the first surface power map 200.

A third example embodiment of the invention provides a third multifocalcontact lens. The third multifocal contact lens is substantially asdescribed in respect of the first embodiment except of the followingfeatures. In this case, the offset in power is not provided by the firstsurface power map, but the offset in power is instead provided by thesecond surface power map. Thus, the first surface power map can be saidto comprise a spiral which does not comprise a variation across theportion. However, the lens power map (being formed by the combination ofthe first and second surface power maps) still comprises a spiral havinga variation across the portion, the variation being imparted by theoffset in power provided by the second surface power map. Thus, thecontact lens of this embodiment provides a lens power map which matchesthat of the first embodiment.

According to a fourth example embodiment of the invention, there isprovided a fourth multifocal contact lens. A first surface power map ofthe fourth contact lens is identical to that of the contact lens of thesecond embodiment. In this embodiment, the second surface power map alsocomprises a spiral formed by a summation of a plurality of components.The plurality of components comprises a first periodic component in aradial direction extending outwards from the centre of the portion and asecond periodic component in an azimuthal direction about the centre ofthe portion. As in the case of the first surface, the spiral comprises aplurality of arms, including peak arms and trough arms. In this exampleembodiment, the periodic components of the second surface power map arethe same as those of the first surface power map. However, a skilledperson will appreciate that alternative embodiments may incorporateperiodic components having different periods on the second surface powermap to one or both of those of the first surface power map. In thisexample embodiment, the second surface power map also comprises acentral region, an outer region, and a transition region.

In this example embodiment, the spiral formed by the second surfacepower map twists in the opposite direction to that formed by the firstsurface power map. Thus, in this particular embodiment, the spiralsprovided by the first surface power map and the second surface power maphave opposing twist directions. In this example embodiment, the spiralformed on the first and second power maps are substantially identicalapart from the opposing twist directions. The power map of the contactlens is determined by the superposition of the first surface power mapand the second surface power map.

FIG. 4 shows a lens power map 300 of the contact lens. The superpositionof the two counter-rotating spirals formed by the first surface powermap and the second surface power map results in a lens power map 300which approximates a pseudo-dartboard pattern of alternating annularrings. The contact lens also provides a monotonic change in the ratio ofthe first lens power to the second lens power as a wearer's pupilconstricts. Thus, the contact lens also provides improved multifocalvision in the presence of variable light conditions. As both the firstsurface power map and the second surface power map comprise central,outer, and transition regions, the overall lens power map 300 of thecontact lens also comprises a central region 303, an outer region 305,and a transition region 307.

According to a fifth embodiment of the invention, there is provided aspectacle lens. The spectacle lens comprises a lens power mapsubstantially as described in respect of the first embodiment of theinvention. It will, however, be appreciated by the skilled person that aspectacle lens does not comprise an optic zone in the same sense as thecontact lenses of the first embodiment. In the case of spectacle lenses,typically substantially all of the lens can be considered to be an opticzone of the lens The skilled person will further appreciate thatcharacteristics of the lens profile defined above in relation to theoptic zone of a contact lens are similarly applicable in relation to theportion of the spectacle lens of the present embodiment. It will beappreciated that alternative embodiments of the invention comprisespectacle lenses having surface power maps substantially as described inrespect of the second, third, and fourth embodiments of the invention.Spectacle lens 700 comprises a central region 715, an outer region 717,and a transition region 719. In this example embodiment, the spiral(s)formed by one or both of the first and second surface power maps do notextend to the left-most edge of the spectacle lens 717. Instead, thespirals only extend out to dashed line 701. It may be that the spiralsdecay in magnitude (for example, linearly) from the boundary between thetransition region 719 and the outer region 717 as they extend outwardsto dashed line 701. In other embodiments, the spirals may havesubstantially constant magnitude across the outer zone 717. In suchembodiments, the spectacle lens 700 may further comprise a narrowblending region running along dashed line 701. It will further beappreciated that, in other embodiments, the spirals continue outwards tothe edges the spectacle lens 700. In this example embodiment, thecentral region 715 (and the surrounding transition region 719 and outerregion 717) is not positioned in the geometric centre of the spectaclelens 700, and can be said to be offset from the geometric centre of thespectacle lens 700. It will be appreciated by the skilled person thatsuch an offset may serve to place the central region in the part of thespectacle lens 700 through which a wearer most frequently looks.

According to a sixth embodiment of the invention, there is provided anintraocular lens. The intraocular lens comprises a spiral powersubstantially as described in respect of the first embodiment of theinvention. It will be appreciated that alternative embodiments of theinvention comprise intraocular lenses having surface power mapssubstantially as described in respect of the second, third, and fourthembodiments of the invention.

FIG. 5 shows a flow chart illustrating the steps of a method 500 ofmanufacturing a lens, for example a contact lens, according to a seventhembodiment of the invention.

A first step of the method 500, represented by element 501, comprisesoperating a lathe to shape a first surface of a portion of one of: alens, a mould for a lens, or an insert for manufacturing a mould for alens. The first surface is shaped such that the first surface variesacross the portion of the lens (which may, for example, be an optic zoneof a contact lens) to form a first surface power map.

A second step of the method 500, represented by element 503, comprisesoperating a lathe to shape a second surface of the portion. That is tosay, the second step comprises operating a lathe to shape a secondsurface of a corresponding (for example, opposing) portion of one of thelens, a mould for the lens, or an insert for manufacturing a mould forthe lens. The second surface is shaped such that the second surfacevaries across at least the portion of the lens to form a second surfacepower map.

The first surface power map and the second surface power map togetherform a lens power map. The first surface power map, the second surfacepower map, or the lens power map comprises a spiral. The spiral variesacross the portion.

It may be that the first surface power map comprises the spiral.Alternatively, or additionally, it may be that the second surface powermap comprises the spiral. It may be that the lens power map comprisesthe spiral (i.e. the spiral is formed by the combination of the firstand second surface power maps). The second surface may be shaped to varyas a mirror image of the first surface. Alternatively, the secondsurface may be shaped such that a spiral formed on the first surfacepower map twists in the opposite direction to a spiral formed on thesecond surface power map.

When the first surface (and the second surface where the second step 503has been performed) are comprised on a mould for a lens or an insert fora mould for a lens, the method 500 may comprise an optional third step,represented by element 505. The third step 505 comprises using the mouldof the insert for a mould for a lens to manufacture a lens.

Whilst the present invention has been described and illustrated withreference to particular embodiments, it will be appreciated by those ofordinary skill in the art that the invention lends itself to manydifferent variations not specifically illustrated herein. By way ofexample only, certain possible variations will now be described.

In the first embodiment a lens having a spiral lens power map wasprovided by a first surface power map of the contact lens comprising aspiral and a second surface power map of the contact lens havingsubstantially constant power across the surface power map. However, inalternative embodiments, a lens having a spiral lens power map isprovided by each of the first surface power map and the second surfacepower map comprising a spiral. In such an embodiment, the periods andphases of the periodic components of the second surface power map arethe same as those of the first surface power map. Thus, the first andsecond surface power maps can be said to comprise mirror images of oneanother. The first and second surface power maps therefore superpose toform a single spiral power map and thereby a contact lens having aspiral lens power map.

In all of the first, second, third, and fourth embodiments, the lenspower maps of the contact lens each comprise a central region havingsubstantially constant power profile, an outer region incorporating thespiral power profile, and a transition region providing a smoothtransition between the central and outer regions. However, somealternative embodiments do not incorporate a transition region. Furtheralternative embodiments do not incorporate distinct central and outerregions. Instead, in such embodiments, the spiral profile extends fromthe centre of the portion of the lens all of the way out to the radialperiphery of the portion.

In the first embodiment, the spiral formed by the first surface powermap twists in an anticlockwise direction. However, in alternativeembodiments, the spiral formed by the first surface power map twists ina clockwise direction. In those embodiments where mirrored spirals areformed on the first and second surface power maps, the spirals mayrotate in either a clockwise or an anticlockwise direction. Similarly,in the fourth embodiment, the spiral formed on the first surface powermap twists in an anticlockwise direction and the spiral formed on thesecond surface power map twists in a clockwise direction. However, inalternative embodiments, the spiral formed on the first surface powermap twists in a clockwise direction and the spiral formed on the secondsurface power map twists in an anti-clockwise direction.

In some embodiments of the invention, the spiral formed on one or bothof the first and second surface power maps changes its direction ofrotation at a pre-determined radial distance from the centre of theportion. For example, the spiral may rotate in a clockwise directionbetween the centre of the portion and the pre-determined radialdistance, and in an anti-clockwise direction beyond the pre-determinedradial distance. In some embodiments, the lens incorporates more thanone change in the direction of rotation of the spiral. Thus, the spiralmay, for example, change from a clockwise rotation to an anti-clockwiserotation before reverting to a clockwise rotation again. It will beappreciated by the skilled person that the lens can incorporate anynumber of changes in the direction of rotation of the spiral. It willalso be appreciated that each of those changes in direction can takeplace at any chosen radial distance from the centre of the portion. Thepower map may therefore comprise annular rings alternating betweenclockwise and anti-clockwise rotating spirals.

In some embodiments, between regions of the ophthalmic lens havingdifferent directions of rotation, there is a region in which the powermap does not vary as a spiral. For example, the region may have asubstantially constant power. For example, from the centre of theportion to a first radial distance, the lens (or surface) power map mayvary as a clockwise rotating spiral, followed by a region ofsubstantially constant power, before varying as an anti-clockwiserotating spiral. The power map may therefore appear to comprise aplurality of annular rings, for example alternating between a spiral andsubstantially constant power, wherein the spiral regions also alternatebetween clockwise and anti-clockwise rotation.

Similarly, in some embodiments, the spiral may be interrupted by one ormore regions, for example rings, in which the power map does not vary asa spiral. For example, the region may have a substantially constantpower. Thus, for example, the power map may comprise annular ringsalternating between a spiral and substantially constant power. In suchembodiments, the spiral may change its direction of rotation betweeneach interruption, or it may continue with its previous direction ofrotation. Thus, the spiral may maintain a constant direction of rotationacross the lens, but the spiral may be interrupted by regions ofsubstantially constant lens power.

Whilst embodiments of the invention have been described above inrelation to a method of manufacturing contact lenses, moulds for contactlenses, or inserts for moulds for contact lenses using a lathe, it willbe appreciated that other methods of manufacture are also possible. Inparticular, the moulds or the inserts may also be manufactured usingadditive manufacturing techniques, for example by 3D printing.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present invention, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the invention that are described as preferable,advantageous, convenient or the like are optional and do not limit thescope of the independent claims. Moreover, it is to be understood thatsuch optional integers or features, whilst of possible benefit in someembodiments of the invention, may not be desirable, and may therefore beabsent, in other embodiments.

The invention claimed is:
 1. A multifocal ophthalmic lens, wherein: afirst surface of the lens is shaped to form a first surface power map; asecond surface of the lens is shaped to form a second surface power map;the first and second surface power maps together form a lens power map;the first surface power map, the second surface power map, or the lenspower map comprises a spiral, the spiral having a variation across atleast a portion of the lens, the spiral having a first periodiccomponent, in a radial direction extending outwards from the centre ofthe portion, and a second periodic component having a substantiallyconstant period, in an azimuthal direction about the centre of theportion.
 2. The multifocal ophthalmic lens according to claim 1,wherein: the first periodic component has a period of greater than 100microns; and the second periodic component has a period of greater than6 degrees.
 3. The multifocal ophthalmic lens according to claim 1,wherein the variation of the spiral comprises an offset in power, theoffset changing according to a radial distance from the centre of theportion.
 4. The multifocal ophthalmic lens according to claim 1, whereina peak power of one or more arms of the spiral varies according to oneor both of: a radial distance from the centre of the portion and anazimuthal position about the centre of the portion.
 5. The multifocalophthalmic lens according to claim 1, wherein: a peak power of each armof the spiral does not vary with radial distance from the centre of theportion; and the peak power of at least one arm of the spiral differsfrom that of the other arms.
 6. The multifocal ophthalmic lens accordingto claim 1, wherein each of the first surface power map and the secondsurface power map vary smoothly across the portion.
 7. The multifocalophthalmic lens according to claim 1, wherein: the portion of the lenscomprises a central region and an outer region, the outer regionsurrounding the central region; the lens power map within the outerregion comprises the spiral; and the lens power map does not varyperiodically within the central region.
 8. The multifocal ophthalmiclens according to claim 7, wherein the central region has a diameter ofless than 50% of that of the portion.
 9. The multifocal ophthalmic lensaccording to claim 7, wherein: the lens comprises a transition region,the transition region surrounding the central region and the outerregion surrounding the transition region; and the lens power map variessuch that the transition region provides a smooth transition between thecentral zone and the outer zone.
 10. The multifocal ophthalmic lensaccording to claim 1, wherein a twist rate of the spiral variesaccording to a radial distance from the centre of the portion.
 11. Themultifocal ophthalmic lens according to claim 1, wherein a width of oneor more arms of the spiral differs from a corresponding width of theother arms of the spiral.
 12. The multifocal ophthalmic lens accordingto claim 11, wherein, at a pre-determined radial distance from thecentre of the portion, the spiral changes its direction of rotation. 13.The multifocal ophthalmic lens according to claim 1, wherein theophthalmic lens is a contact lens, a spectacle lens, or an intraocularlens.
 14. A method of manufacturing a multifocal ophthalmic lens, themethod comprising: operating a lathe to shape a first surface of one of:a lens, a mould for a lens, or an insert for manufacturing a mould for alens to form a first surface power map; operating a lathe to shape asecond surface of the lens, mould, or insert to form a second surfacepower map; wherein: the combination of the first and second surfacepower maps forms a lens power map; the first surface power map, thesecond surface power map, or the lens power map comprises a spiral, thespiral having a variation across at least a portion of the lens, mouldor insert, the spiral having a first periodic component, in a radialdirection extending outwards from the centre of the portion, and asecond periodic component having a substantially constant period, in anazimuthal direction about the centre of the portion.
 15. A method ofimproving vision of a person, the method comprising: providing themultifocal ophthalmic lens according to claim 1 to a person in need ofimproved vision.
 16. The multifocal ophthalmic lens according to claim1, wherein the ophthalmic lens is a centre distance contact lens, or acentre near contact lens.
 17. The multifocal ophthalmic lens accordingto claim 7, wherein the central region has an optical powercorresponding to a distance vision correction.
 18. The multifocalophthalmic lens according to claim 7, wherein the central region has anoptical power corresponding to a near vision correction.